First‐order control of syntectonic sedimentation on crustal‐scale structure of mountain belts

Abstract

AbstractThe first‐order characteristics of collisional mountain belts and the potential feedback with surface processes are predicted by critical taper theory. While the feedback between erosion and mountain belt structure has been fairly extensively studied, less attention has been given to the potential role of synorogenic deposition. For thin‐skinned fold‐and‐thrust belts, recent studies indicate a strong control of syntectonic deposition on structure, as sedimentation tends to stabilize the thin‐skinned wedge. However, the factors controlling basement deformation below fold‐and‐thrust belts, as evident, for example, in the Zagros Mountains or in the Swiss Alps, remain largely unknown. Previous work has suggested that such variations in orogenic structure may be explained by the thermotectonic “age” of the deforming lithosphere and hence its rheology. Here we demonstrate that sediment loading of the foreland basin area provides an additional control and may explain the variable basement involvement in orogenic belts. When examining the role of sedimentation, we identify two end‐members: (1) sediment‐starved orogenic systems with thick‐skinned basement deformation in an axial orogenic core and thin‐skinned deformation in the bordering forelands and (2) sediment‐loaded orogens with thick packages of synorogenic deposits, derived from the axial basement zone, deposited on the surrounding foreland fold‐and‐thrust belts, and characterized by basement deformation below the foreland. Using high‐resolution thermomechanical models, we demonstrate a strong feedback between deposition and crustal‐scale thick‐skinned deformation. Our results show that the loading effects of syntectonic sediments lead to long crustal‐scale thrust sheets beneath the orogenic foreland and explain the contrasting characteristics of sediment‐starved and sediment‐loaded orogens, showing for the first time how both thin‐ and thick‐skinned crustal deformations are linked to sediment deposition in these orogenic systems. We show that the observed model behavior is consistent with observations from a number of natural orogenic systems.